The invention likewise relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention for preparing flame retardants.
Process for preparing salts of dialkylphosphinic acids
The invention relates to a process for preparing salts of dialkylphosphinic acids and to the use of the dialkylphosphinate salts prepared by this process.
Aluminum salts of organic phosphorus-containing acids are known as flame retardants. They can be prepared by various processes.
EP-A-0 299 922 describes a process for preparing aluminum salts of phosphoric and phosphonic esters by reacting aluminum with phosphoric acid, phosphonic acid or an ester thereof.
In the process described in EP-A-0 245 207, aluminum compounds are reacted with alkylphosphonic diesters to give the corresponding aluminum salt.
According to EP-A-0 327 496, the reaction of aluminum hydroxide with alkylphosphonic diesters in the absence of water at approximately 180xc2x0 C. likewise leads to aluminum salts of phosphonic half-esters.
EP-A-0 699 708 describes flame-retardant polyester molding compounds, the polyesters being given a flameretardant finish by adding calcium salts or aluminum salts of phosphinic. or diphosphinic acids. The abovementioned salts are obtained by reacting the corresponding dialkylphosphinic acids with calcium hydroxide or aluminum hydroxide.
DE 24 47 727 describes low-flammability polyamide molding compounds which comprise a salt of a phosphinic acid or of a diphosphinic acid.
However, the abovementioned processes have the disadvantage that the suitable organic phosphorus compounds must first be prepared in a laborious manner. This applies, in particular, to the dialkylphosphinic acids, whose aluminum salts give the best results in the application as flame retardants, and for which, likewise, some synthetic pathways are described.
Thus DE 21 00 779 Al describes a process for preparing alkyl dialkylphosphinates by addition of olefins having from 2 to 22 carbon atoms to alkylphosphonous esters.
In this case also, there has been the lack to date of an economic synthesis method which leads to homogeneous products in a high yield.